1. Field of the Invention
The present invention relates to an apparatus and method for measuring the convective heat transfer coefficients of nanofluids.
2. Description of the Related Art
A nanofluid is a mixed fluid configured to add a small quantity of nano-sized solid particles having very high thermal conductivity to a base fluid, such as water or ethylene glycol, for heat transfer purposes, thereby increasing the thermal conductivity of the fluid, with the result that the overall heat transfer performance is improved. Therefore, the degree of improvement of heat transfer performance of a nanofluid appearing after the mixing of the particles, compared to that of the initial base fluid, must be quantitatively measured.
The determination of thermal performance of a nanofluid in conventional technology was conducted in such a way as to measure thermal conductivity in a static state and to primarily determine whether there is a possibility of improving heat transfer performance of the nanofluid. However, the addition of nanoparticles to a fluid generally accompanies an increase in viscosity along with an improvement of thermal conductivity. Due thereto, the thermal conductivity of a nanofluid is improved, but more pump power may be required to drive such a nanofluid. A nanofluid is a medium to be used in a convective heat transfer state, that is, in the state in which the flow of a fluid is present. According to the theory of convective heat transfer, thermal conductivity is one of a plurality of variables influencing convective heat transfer, and thus determining the performance of a nanofluid by measuring only thermal conductivity results in a plurality of problems in actual application. Therefore, in order to determine the ultimate thermal performance of a nanofluid, an experiment for measuring a convective heat transfer coefficient is required.
A representative experimental device for measuring a convective heat transfer coefficient may be a double pipe heat exchanger or an internal flow device using a heated pipe. However, since this experimental device also includes peripheral devices such as a thermostat and a pump, it has a complicated structure and a large size. Therefore, many difficulties are encountered in the evaluation of the convective heat transfer performance of a nanofluid. Further, unlike the measurement of thermal conductivity performed in a static state, the convective heat transfer experiment is problematic in that a lot of cost and time is required, and large errors may be included in the ultimately calculated convective heat transfer coefficient depending on the circumstances.
In detail, the conventional convective heat transfer experiment is problematic in that a lot of manufacturing time and cost is required in order to acquire an amount of nanofluid sample sufficient to fill the inside of the device, and in that, when it is desired to replace a sample, it is difficult to wash the inside of the device. Further, there is an additional problem in that, when the precision of acquired data and heat loss occurring in a measurement procedure are not accurately calculated, uncertainty included in a convective heat transfer coefficient increases. Furthermore, such a conventional convective heat transfer experiment is also problematic in that, when samples must be discarded, additional cost and environmental pollution occur.